Polymer dispersants and methods of use in a nuclear steam generator

ABSTRACT

A novel high-purity polymer dispersant and sludge conditioner added to the feedwater entering the secondary side of a nuclear steam generator for minimizing the accumulation of metal-oxide deposits within the nuclear steam generator during the continuing operation of the generator is disclosed. The high-purity polymer is selected from a group consisting of acrylic acid polymer, methacrylic acid polymer, acrylate polymer, methacrylate polymer, copolymers, and terpolymers, acrylate/acrylamide copolymer, acrylate/methacrylate copolymer, terpolymers, and mixtures thereof. Methods of making and applying the polymer dispersant and sludge conditioner are described. Means for removing the metal oxides and polymer from the blowdown stream are disclosed.

This is a divisional of application Ser. No. 08/677,464 filed Jul. 10,1996 U.S. Pat. No. 5,864,596.

BACKGROUND OF THE INVENTION

The present invention relates to novel methods and materials forminimizing metal-oxide deposits on steam generator tubes in thesecondary side of pressurized nuclear steam generators by utilizingspecific high-purity polymer dispersants.

At present, no method or process exists for eliminating and preventingthe deposit of metal-oxides/sludge in the secondary side of nuclearsteam generators during operation of the generator. The only method andprocess existing for controlling the amount of impurities that enterinto the secondary side of the steam generator is the utilization ofpure water. The consequences resulting from the buildup of metal oxideswithin the secondary side of a steam generator are reduced steam outputthereby resulting in lost electrical output from the generating plant,increased water level fluctuations within the steam generator therebyresulting in lower steam and electrical output, and the initiation ofcorrosion deposits within the heat exchanger through the concentrationof the dissolved chemical species from the secondary water. Thecorrosion within the secondary side of a pressurized nuclear steamgenerator ultimately may result in tube plugging and sleeving and theeventual loss of electrical output because of lost heat transfer or flowimbalances unless the steam generators themselves are replaced at a costof approximately $200,000,000 per plant.

Accordingly, all known processes for eliminating deposits of metaloxides in the secondary side of recirculating steam generators have beendirected to the removal of these deposits after they build-up in theheat exchanger. The major technique utilized for the removal ofsuspended and dissolved impurities from the secondary side of therecirculating steam generator involves removing a portion of the waterfrom the steam generator during operation on a continuous or periodicbasis through a blowdown system. Typically, the blowdown system onlyremoves up to 10 percent of the total metal oxides or impurities whichenter the recirculating nuclear system generator during operation, withthe remaining metal oxides or impurities continuing to build-up and tobe deposited within the secondary side of the recirculating nuclearsteam generator. This deposition may result in pressure loss, levelfluctuations, and corrosion of the secondary side of the nuclear steamgenerator.

Several mechanical and chemical methods have been suggested for removingmetal oxides or impurities from within the secondary side of nuclearsteam generators when the system is near or at shutdown conditions. Oneof these methods utilizes sludge lancing at shutdown which employs highpressure water to flush loosely adhered oxide deposits and sludge fromthe lower tube sheet of the nuclear steam generator. This processtypically does not address deposition of corrosion in the upper tubesupport plates and does not clean any clogged crevices on the secondaryside of the nuclear steam generator. The percentage of metal oxides orcorrosion removed by this process is about two percent of the totaloxides entering the nuclear steam generators over a typical 18-monthfuel cycle. The cost of completing a sludge lancing is approximately$350,000 for each 18-month fuel cycle in a typical four-loop plant.

Another method suggested for removing metal oxides/sludge at shutdownfrom the secondary side of a nuclear steam generator is the bundle-flushprocess. This process entails directing flush water from the upper partof the recirculating nuclear steam generator to remove the loose sludgefrom the upper tube support plates. The cost of the bundle flush processis approximately $500,000 per application; however, the process onlyremoves the soft, loosely adhered sludge, and does not remove sludgewhich is strongly adhered to the heat transfer surfaces. Additionally,the small crevices within the heat transfer structure are not cleaned atall by this process. Accordingly, this process is of limited value anddoes not overcome the problem of removing strongly adhered deposits orimpediments within the heat-transfer structure.

Crevice flush techniques have been suggested in an attempt to open orclean closed or packed crevices by heating the secondary side of thenuclear steam generator above a boiling point with an inert atmosphereoverpressure and then releasing this overpressure. The crevice flushprocess results in a boiling action which purportedly flushes theimpurities from the crevices in the nuclear steamed generator. However,this method has only demonstrated limited effectiveness and is very timeconsuming, thereby prolonging downtime, an added cost in the electricalindustry.

Chemical-soak techniques have been suggested for use during shutdown topromote removal of loose sludge and loosely adhered deposits within thenuclear steam generator. The chemical soaks employ amines such asdimethylamine and morpholine. These soaks have exhibited limitedeffectiveness in removing loosely adhered deposits, and the amount orpercentage of metal oxides removed is less than acceptable. Theadvantage of this process is that the cost is low; but the disadvantagesof this method are that the process is time consuming, and theeffectiveness and the amount of metal oxides removed is less thansatisfactory.

Pressure-pulse cleaning or water slapping are mechanical methods whichare utilized during an outage or shutdown for removing loosely adheredsludge from the upper tubes or the tube support plates of the nuclearsteam generator. The sludge or deposits are removed by raising the wateron the secondary side to a desired level and then injecting a highpressure gas such as nitrogen into the water. The bursting of thebubbles as the gas approaches the surface of the water partially removeslimited amounts of the loosely adhered sludge or oxide deposits. Thistechnique may increase the amount of metal oxides removed from 5-15percent of the total amount of metal oxides deposited within the nuclearsteam generator; however, this method does not remove hard deposits anddoes not open crevices packed with metal oxides or other corrosion. Thecost of a pressure pulse cleaning is typically $200,000 to $600,000 perunit. It is recommended that such a cleaning be employed everyone-to-four refueling cycles.

Finally, the methods of chemical cleaning at low or high temperaturesand the use of chemically enhanced pressure pulse cleaning are processesutilizing specific organic materials that dissolve the metal-oxidedeposits within the nuclear steam generator. The cleaning solutiondissolves the metal-oxide deposits, and the spent cleaning solution mustbe processed and properly disposed. The chemical-cleaning processes maybe selected to remove specific metal oxides contained within the nuclearsteam generator. Variations of the chemical cleaning process include theheating of the cleaning solution above the liquid-boiling temperatureunder an inert atmosphere and then releasing the pressure to forceboiling in the cracks and the crevices and the use of pulse-cleaningtechniques to promote circulation and movement of the cleaning solution.The chemical cleaning processes remove virtually one-hundred percent ofthe metal-oxide deposits within the secondary side of the recirculatingsteam generator, but at a cost of between $5,000,000-$10,000,000 percleaning. Many of the nuclear generating plants in operation may requirechemical cleaning at least once during their lifetime.

Thus, each of the mechanical prior art methods for removing metal-oxidesfrom the secondary side of the nuclear steam generator is directed toremoving the loosely deposited oxides within the heat-exchange structurethat results from the continued operation of the nuclear power plant.Although chemical cleaning removes substantially all metal oxides, sucha process is extremely expensive and time consuming. Accordingly, noneof the known chemical or mechanical methods is directed to preventingthe deposition or formation of sludge within the secondary side of anuclear steam generator during operation of the generator. Theseprocesses attempt to remove the oxide and corrosive deposits after theyhave been deposited in the secondary side of the nuclear steamgenerator, processes which are extremely costly and which result insignificant downtime of the nuclear power plant.

Natural polymer dispersants have been used to minimize deposition ofsludge deposits in fossil steam generators since the early 1900's, andsynthetic polymers have been recently utilized for metal-oxidedispersing and sludge conditioning in fossil steam generators. However,such synthetic polymers have not been qualified for use in minimizingmetal-oxide deposition on the secondary side of recirculating nuclearsteam generators. Most synthetic polymers developed and used today inwater-treatment applications are manufactured using inorganics, such assodium persulfate, as the initiators of polymerization, and otherinorganics as chain transfer agents. However, the sodium and persulfateinorganics contribute unwanted contaminants in significant excess tothose required for application in nuclear steam generator units.Polymers typically used in boilers contain inorganic solids atconcentrations up to 500 times the allowable levels for application tonuclear steam generator units. Inorganic impurities can include sodium,potassium, chlorine, sulfur, fluorine, and phosphorus—elements which areparticularly objectionable and damaging when used in nuclear steamgenerator operations.

Synthetic polymers used in water treatment applications are typicallyneutralized with sodium or potassium, forming the inorganic salt.Although ammonia-neutralized versions have been used to a small extent,ammonia is a known copper-alloy corrodent. Polymer neutralizationminimizes system upset potential. Polymers have been used unneutralized,but the feed-rate variations have been known to cause system upsets bylowering the pH, thereby resulting in corrosion to the operating system.

SUMMARY OF THE INVENTION

It is one object of the present invention to provide a method andprocess of substantially preventing the formation of sludge, corrosion,or metal-oxide deposits within the secondary side of nuclear steamgenerators during all phases of operation.

It is another object of the present invention to provide a method ofsubstantially preventing the formation of sludge, corrosion, ormetal-oxide deposits within the secondary side of nuclear steamgenerators during all phases of operation by utilizing the applicationof a high-purity polymer dispersant to the feedwater entering thesecondary side of nuclear steam generators.

It is still another object of the present invention to apply ahigh-purity polymer dispersant to the feedwater entering the secondaryside of nuclear steam generators, wherein the high purity polymerdispersant is selected from a group consisting of acrylic acid polymer,methacrylic acid polymer, acrylate polymer, methacrylate polymer,copolymers, terpolymers, and mixtures thereof.

It is still another object of the present invention to select ahigh-purity polymer dispersant from a group consisting ofacrylate/acrylamide copolymer, acrylate/methacrylate copolymer,terpolymers, and mixtures thereof.

It is still another object of the present invention to utilize qualifiedhigh-purity polymer dispersants added to the feedwater entering thesecondary side of nuclear steam generators to prevent the formation ofsludge, corrosion, or metal-oxide deposits within the secondary side ofnuclear steam generators.

It is still another object of the present invention to utilize achemically pure polymer dispersant combination to remove metal-oxidecorrosion deposits within nuclear steam generators and to prevent theformation of such corrosion deposits during the operation of nuclearsteam generators.

It is still another object of the present invention to prepare ahigh-purity polymer dispersant using non-inorganic initiators,terminators, and neutralizers for use in preventing the formation ofsludge, corrosion, or metal-oxide deposits within the secondary side ofnuclear steam generators.

It is still another object of the present invention to prepare ahigh-purity polymer dispersant having a high purity and molecular weightsufficient to render the polymer dispersant thermally stable withsufficient dispersant activity under a pressure of 1300 psi or less anda temperature corresponding to the saturation temperature at 1300 psi.

It is still another object of the present invention to minimize systemupsets in nuclear steam generators by neutralizing the high-puritypolymer dispersant with amines, such as, monoethanolamine, morpholine,dimethylamine, 3-methoxypropylamine, diethanolamine,diethylaminoethanol, diemrthylpropanolamine, cyclohexylamine,2-amino-2-methyl-1-propanol, triethanolamine, 3-hydroxyquinuclidine and5-aminopentanol to maintain a pH level of about 9.5 in the steamgenerators.

It is still another object of the present invention to utilize ahigh-purity polymer dispersant mixed with the feedwater entering thesecondary side of a pressurized water reactor steam generators operatingin a pressure range of 500 to 1300 psi to prevent the formation ofmetal-oxide corrosion deposits during the operation of the nuclear powerplant.

It is still another object of the present invention to utilizehigh-purity polymer dispersants which may contain sulfur-containingactive groups or phosphorus-containing active groups which can bequalified to meet the necessary water quality specifications and whichmay be used to provide removal of metal oxides from the nuclear steamgenerator during shutdown.

It is still another object of the present invention to utilize methodssuch as filtration with specialized filter media by varying theeffective pore sizes and zeta potential to remove residual polymerdispersant and complexed metal-oxide/polymer dispersant from thedischarge blowdown water for recycling.

It is still another object of the present invention to utilize charcoalor activated carbon filters to remove residual polymer dispersant andcomplexed metal-oxide/polymer dispersant from the discharged blowdownwater for recycling through the system or ultimate discharge to areceiving stream.

It is still another object of the present invention to utilize methodssuch as demineralization to remove the residual-polymer dispersant andcomplexed metal-oxide/polymer dispersant from the discharged blowdownwater for use as recycled feedwater for steam generation within thenuclear plant or ultimate discharge to a receiving stream.

It is still another object of the present invention to utilizepurification and ultrafiltration methods, such as flocculation,coagulation, reverse osmosis, and ultrafiltration to remove the residualpolymer dispersant and complexed metal-oxide/polymer dispersant from thedischarged blowdown water prior to recycling or ultimate discharge to areceiving stream.

The present invention relates to the utilization of selected high-puritypolymer dispersants for preventing the formation of deposits of metaloxides within the secondary side of a nuclear steam generator in allmodes of operation. The polymer dispersant is selected from a groupconsisting of acrylic acid polymer, methacrylic acid polymer, acrylatepolymer, methacrylate polymer, copolymers, terpolymers, and mixturesthereof, acrylate/acrylamide copolymer, acrylate/methacrylate copolymer,terpolymers, and mixtures thereof. Specifically, the polymer dispersantmay be the polymer monounsaturated carboxylic acid or the polymersulfonated styrene polymer, and copolymers. Also, it is within the scopeof the present invention that polymer dispersants or polymer-dispersantblends having sulfur-containing and phosphorus-containing functionalgroups or mixtures thereof may be utilized for iron transport andremoval from the nuclear steam generator during shutdown or operation ofthe nuclear power reactor.

The polymer dispersant used in the present invention is of sufficientpurity wherein the resultant chemical analysis of the discharge from thesecondary side of the nuclear steam generator through the blowdownsystem yields a concentration of sodium, potassium, calcium, magnesium,chloride, sulfate, silicate, and phosphate ions of less than about 10parts per billion of each ion in the blowdown during normal operation.

Additionally, the polymer dispersants utilized in the present inventionas an additive to the feedwater entering the secondary side of a nuclearpower generator possess metal-oxide dispersive and sludge conditioningcharacteristic of approximately 1 to 1,000 parts polymer dispersant toremove and prevent the buildup of one part iron oxide, the predominantmetal oxide contained in the metal-oxide/sludge discharge from thenuclear steam generator. However, the polymer-dispersant concentrationdepends upon the amount of iron oxide in the feedwater stream and theconcentration of the polymer initially used as the additive and is,preferably, within the range of 1 to 25 parts polymer versus one partiron oxide. The measured cation conductivity of the steam exiting thesecondary side of the nuclear power generator and entering the turbine,corrected to 25° C., should be equal to or less than 1.0 μS/cm. Finally,the metal-oxide transport, or degree of the removal of iron oxide fromthe feedwater entering the secondary side of the nuclear powergenerator, as contained in the blowdown stream, is equal to or greaterthan a five percent increase than when the system does not contain thedisclosed polymer dispersant or dispersants.

The invention further consists of certain novel features and chemicaldetails hereinafter fully described, and illustrated in the accompanyingdrawing and particularly pointed out in the appended claims, it beingunderstood that various changes and details may be made withoutdeparting from the spirit, or sacrificing any of the advantages of thepresent invention.

DESCRIPTION OF THE DRAWING

For the purpose of facilitating and understanding the present invention,it is illustrated in the accompanying drawing the preferred embodimentof the present invention hereof, from an inspection of which, whenconsidered in connection with the following description, the invention,its operation, and many of its advantages, will be readily understoodand appreciated.

FIG. 1 is a schematic diagram illustrating the components of a nuclearpower plant and the application of the novel polymer dispersant to thefeedwater entering the secondary side of the nuclear power plant toremove and to prevent the formation of sludge, corrosion, or metaloxides therein in accordance with the present invention.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a nuclear power station 10 which iscomprised of a reactor 12 operatively connected to a steam generator 14wherein the heat from the reactor is directed through a conduit 13 intoheat exchanger tubes 15 within the steam generator 14. The reactor heatsthe feedwater entering the secondary side 16 of the steam generator inthe steam-drum portion 18 of the steam generator to produce thesaturated steam leaving the secondary side through conduit 19 to drive aturbine 20 and generator 22, as is known in the art. The spent-heatedsteam exiting the turbine 20 is directed through a conduit 23 to acondenser 24 under vacuum, wherein the circulating steam/feedwater iscooled. The cooled feedwater exits the condenser 24 via conduit 26 andpasses through a series of extractors and low and high pressure heaters27 for heating the recycled feedwater and returns via conduit 28 to thesecondary side of the nuclear steam generator, as is known in the art.Appropriately, pumps 29 are provided to facilitate cycling of thesystem. A blowdown conduit 30 exits the lower secondary side of thenuclear steam generator 14 for facilitating and for permitting removalof impurities that build up within the nuclear steam generator. Theblowdown material exiting the secondary side of the nuclear steamgenerator is filtered by a series of filtering means 32, which mayinclude charcoal, activated carbon, mesh filter, ultrafiltration, orreverse osmosis, chemically analyzed through sampling ports 40, and thenreturned to the condenser 24 under vacuum through conduit 36 for furtherpurification and then returned as feedwater entering the secondary sideof the nuclear reactor in the same manner as has been discussed with thesteam/feedwater. In the alternative, the blowdown material may bedirected via valve 41 through conduit 30′ to various filter means 32′for filtering the treated waste material to permit the material to bedischarged into a receiving stream 38.

The blowdown method of removing the oxides and impurities within thesecondary side of the steam generator in accordance with the prior arttechniques only removes up to 10 percent of the total metal oxides thatbuild up within the secondary side of the nuclear steam generator 14.Importantly, the present invention utilizes the identification ofselected high purity polymer dispersants which, when added to thefeedwater entering the secondary side of the nuclear steam generator,prevent the accumulation of metal oxides within the secondary side ofthe nuclear steam generator during operation of the generator andsubstantially increase the metal oxides removed from the nuclear steamgenerator.

The novel polymer dispersants and sludge conditioners utilized in thepresent invention are selected from a group consisting of acrylic acidpolymer, methacrylic acid polymer, acrylate polymer, methacrylatepolymer, copolymers, terpolymers, thereof. Also, the polymer dispersantmay be selected from a group consisting of acrylate/acrylamidecopolymer, acrylate/methacrylate copolymer, and terpolymers and mixturesthereof. Specifically, the polymer dispersant may be monounsaturatedcarboxylic acid or the polymer or copolymers of sulfonated styrene. Itis within the scope of the present invention that polymer disperants orpolymer dispersant blends having sulfur-containing andphosphorus-containing functional groups or mixtures thereof may beutilized in the present invention for iron transport and removal fromthe nuclear steam generator 14 during shutdown or operation of thenuclear power reactor.

The polymer dispersants used in the present invention possess a highpurity wherein the resultant chemical analysis of the filtered andcleaned blowdown discharge from the secondary side of the nuclear steamgenerator yields a concentration of sodium, potassium, calcium,magnesium, chloride, sulfate, silicate, and phosphate ions of less thanabout 10 parts per billion of each ion during normal operation.Preferably, the chemical analysis of each of the ion concentrations inthe blowdown discharge should be in the range of about one part perbillion or less.

During normal operation, the iron concentration in feedwater istypically less than five parts per billion. However, during non-steadystate operation, for example during a unit startup, the feedwater ironconcentration may be elevated to several hundred parts per billion. Thepolymer dispersants in accordance with the present invention minimizemetal oxide fouling and deposition and provide sludge conditioning innuclear steam generators. Sludge conditioning allows for enhancedremoval of metal oxides during sludge lancing of steam generators. Thesehigh-purity polymers minimize the amount of inorganic contaminants tothe feedwater of nuclear steam generating units and in the blowdownafter concentration in the secondary side of the units. The polymerproduct inorganic contaminant level must not exceed 100 parts permillion total inorganic solids when the steam generator water is cycled100 times and must not exceed 30 parts per million when cycled 300times. These requirements are based on the necessity that the productcontaminant level not exceed 10 parts per billion in the blowdown and,preferably, less than one part per billion. In combination with all ofthe above restrictions, the resulting polymer must be thermally stableat system-operating pressures and temperatures and low-operating pH(9.5) and capable of dispersing metal oxides, such as iron oxide. Anespecially preferred embodiment of the present invention is thepolymeric composition produced when hydrogen peroxide or other organicperoxides are used as initiators for the polymerization of acrylic acid,methacrylic acid, and other known useful monomers for the presentinvention. Additional initiators which produce no inorganic contaminantsinclude benzoyl peroxide (tradename LUCIDOL 78 available from ElfAtochem), acetyl peroxide, succinic acid peroxide, lauroyl peroxide(tradename Alperox-F available from Elf Atochem), decanoyl peroxide(tradename Decanox-F available from Elf Atochem), hydrogen peroxide,2,2′ azobis (2-methylpropanenitrile) (tradename Vazo 64 available fromDuPont), 2,2′ azobis (2-methylbutanenitrile) (tradename Vazo 67available from DuPont), t-Butyl peroctoate, t-Butyl peroxyiso butgrate(tradename Lupersol 80 available from Elf Atochem), t-butylperoxyprivalate (tradename Lupersol 11 available from Elf Atochem), and4,4′-azobis (4-cyonovaleric acid) (tradename V-501 available from Wako).Hydrogen peroxide and other organic peroxides and organic initiators donot contribute inorganic contaminants but unexpectedly produce aneffective polymeric dispersant and sludge conditioner for metal oxideswhich is substantially free of inorganic solids.

The concentration of polymer dispersant utilized in the presentinvention as an additive to the feedwater entering the secondary side ofthe nuclear steam generator possesses a metal oxide dispersivecharacteristic of approximately 1 to 1,000 parts polymer dispersant toremove and to prevent the buildup of one part iron oxide within thegenerator. However, the preferred range is between about 1 to 25 partsdispersant. Iron oxide is the predominant metal oxide contained in thedischarge from the nuclear steam generator. Accordingly, theconcentration levels of the polymer dispersant depends upon the amountof iron oxide present in the feedwater and the concentration of thepolymer dispersant initially used as the polymer-dispersant additive.

As pointed out above, it is also within the scope of the presentinvention that the novel polymer dispersants useful in the presentinvention may contain functional groups containing sulfur and/orphosphorus which, although they break down during the passage throughthe nuclear steam generator and compromise secondary-water quality andincrease corrosion potential, such active groups within the polymerdispersant may be used where the breakdown does not increase theconcentration of Na, K, Ca, Mg, Cl, SO₄, Si, and PO₄ ions greater thanabout 10 parts per billion.

The measured cation conductivity through sampling port 19′ of the steamexiting the secondary side of the nuclear power generator 14 throughconduit 19 should be equal to or less than 1.0 μS/cm when converted to25° C. The metal-oxide transport or the removal of the metal oxide fromthe feedwater entering the secondary side of the nuclear power generatorcontained in the blowdown system is equal to or greater than a fivepercent increase when the system does not contain the disclosed polymerdispersants.

One example of a high-purity polymer dispersant useful in the presentinvention is a polyacrylic-acid polymer dispersant designated as PolymerA, and was prepared as follows:

Into a glass-lined reactor was placed 64.38 parts demineralized water,20.60 parts glacial acrylic acid, and 10.94 parts isopropanol, as thechain-transfer agent, with stirring. A nitrogen sparge was begun andbubbled through the stirred solution for 15 minutes. The temperature wasraised to 88° C., and 4.08 parts hydrogen peroxide (35 percent) wasadded. Under nitrogen blanket, the temperature was maintained at 88° C.for 5½ hours. Cooling may be used if the temperature exceeds 92° C. Atthe end of the reaction, the isopropanol was stripped off the reactionproduct and the measured temperature was 96° C. Cooling was begun and aproportional amount of demineralized water was added to compensate forthe removal of the isopropanol-water mixture. The final productdesignated as Polymer A was free of inorganic solids, contained only 100parts per million isopropanol, possessed 20 percent solids and had ameasured pH of 2. The weight average molecular weight of Polymer A was135,000. Analysis of Polymer A showed it to contain chloride <2 ppm,sodium <10 ppm, sulfur <5 ppm, phosphorus <5 ppm, and potassium <10 ppm.Polymer A demonstrated excellent thermal stability after exposure fortwo hours at 900 psig and 277° C., using hydrazine as the oxygenscavenger.

Another example is the preparation of a high-purity polyacrylic acidwithout the use of isopropanol as the chain-transfer agent. Into aglass-lined reactor was placed 34.34 parts demineralized water and 16.09parts glacial acrylic acid with stirring. A nitrogen sparge was begunand bubbled through the stirred solution for 15 minutes. The temperaturewas raised to 80° C., and 27.89 parts hydrogen peroxide (35 percent) wasslowly added. The temperature climbed to 88° C. Cooling was applied sothe temperature would not exceed 91° C. Under nitrogen blanket, thetemperature was raised to 95° C. and held at this temperature for 5¼hours. The product was then cooled to room temperature, and 21.68 partsmonoethanolamine was slowly added with cooling. The monoethanolaminesalt of polyacrylic acid, designated as Polymer B, was free of inorganicsolids and contained 20.5 percent solids. The product had a measured pHof 10.2 and a weight-average molecular weight of 138,000. Thus, it iswithin the scope of the present invention that the polymer dispersantand sludge conditioner may have a weight-average molecular weight ofabout 1,000,000 or less, with the preferred weight-average molecularweight being between about 70,000 to 150,000.

To measure the effectiveness of high-purity polymers for dispersing ironoxide, the precipitated iron (5 ppm Fe) in the test was prepared in situas iron hydroxide at pH 11. A dosage of 6 ppm active polymer was added,and the resulting mixture was refluxed for three hours prior to asettling test. A good iron dispersant will maintain most of the ironsuspended in solution after a 23-hour settling period. Results of thetests are given in Table 1 below:

TABLE 1 Brookfield Viscosity Iron of Treatment, Dispersion % Dis-Treatment cps ppm persion Polyacrylates Polymer A 275 4.25 85 Polymer B613 2.76 55 Polymer C 515 4.37 87 Polymer D 1,215 4.34 87 Polymer D1,312 4.37 87 Polymer E 3,340 4.44 89 Polymer F 8,820 4.29 86 Polymer G63,500 3.71 74 Polymethacrylates Polymer I 910 3.37 67 Polymer J 2,4004.65 93 Acrylate/Methacrylate Copolymer Polymer K (80/20)* 348 4.26 85Polymer L (70/30)* 260 4.72 94 Polymer M (60/40)* 1,135 4.64 93Acrylate/Methacrylate/t Butyl Acrylamide Terpolymer Polymer N (65/30/5)*270 4.08 81 Polymer O (60/30/10)* 265 4.51 90 Acrylate/Methacrylate/Maleic Acid Terpolymer Polymer P (65/30/5)* 393 4.55 91 Polymer Q(60/30/10)* 237 4.25 85 Polymer R 750 0.46 9 *(By mole)

As shown in the above table, the high-purity polymers (Polymers A-Q) arehighly effective dispersants for iron oxide, whereas Polymer R wasrelatively ineffective. The Polymer A-Q contain 19-21 percent solids.Polymer R was a commercial 45 percent solution of polyacrylic acid madeusing sodium persulfate as the initiator containing 2.9 percent sodium.The metal oxide removal percent is calculated as follows:${{MOR}\quad \%} = {{\frac{\left( {{Metal}\quad {oxide}\quad {{conc}.\quad {in}}\quad {blowdown}} \right)\quad \quad \left( {{Mass}\quad {flow}\quad {rate}\quad {of}\quad {blowdown}} \right)}{\left( {{Metal}\quad {oxide}\quad {{conc}.\quad {in}}\quad {feedwater}} \right)\quad \quad \left( {{Mass}\quad {flow}\quad {rate}\quad {of}\quad {feedwater}} \right)} \cdot 100}\%}$

Thus, in typical nuclear steam generators, the MOR percent is about fivepercent without the polymer-dispersant treatment. Table 1 demonstratesthe effectiveness in dispersing iron oxides through the system. Forexample, Polymer A dispersed 85 percent, a 1700 percent increase.

Polymer A has been chemically analyzed and calculated to contributesodium, potassium, calcium, magnesium, chloride, sulfate, silicate, andphosphate ion concentrations in the blowdown discharge of less thanabout 10 parts per billion, and, preferably, less than one part perbillion.

Another factor to consider in selecting the appropriate polymerdispersant is the breakdown rate or thermal stability of the polymerdispersant under nuclear steam generator conditions versus the residencetime of any species entering the nuclear steam generator. The residencetime is calculated as follows: Residence Time=7·t_(½) where t_(½) is thehalf-life of the cleanup system.

t_(½) =ln(2)·^(M) _(SG)/^(m) _(BD)

where ^(M) _(SG)=The Mass of liquid in steam generator, (lbs.)

and ^(m) _(BD)=The Mass flow rate of blowdown, (lbs./hr.)

For a typical nuclear steam generator:

^(M) _(SG)=100,000 lbs. of liquid at full power

^(m) _(BD)=33,000 lbs./hr.

which yields a half-life t_(½) of 2.1 hours and a residence time of 14.7hours. A residence time of 14.7 hours means that the quantity of polymerdispersant entering the generator is not measurably detectable after14.7 hours. The breakdown rate of the polymer is based on refreshedautoclave testing which determined polymer concentrations as a functionof time. The polymer dispersant possessed the desired thermal stabilityfor use in the nuclear steam generator.

The thermal stability of high-purity polymers was determined bymeasuring the activity of the polymers for dispersing iron oxide beforeand after autoclaving for four hours at 900 psig and 530° F. The testsolution was adjusted to a pH of about 9.5 using diethanolamine. Resultsof the tests obtained at a polymer dosage of 10 ppm active are given inTable 2:

TABLE 2 Iron Dispersion, ppm Treatment Before Autoclaving AfterAutoclaving Polymer C 4.35 4.69 Polymer D 4.38 4.66 Polymer E 4.32 4.63Polymer F 4.44 4.50 Polymer H 4.33 4.67

The performance of the high-purity polymers (Polymers C, D, E, F, and H)is not adversely affected by autoclaving under high pressure andhigh-temperature conditions.

The high-purity polymers are preferably neutralized with an amine foraddition to the secondary side of a nuclear steam generator fordispersing metal oxides. Suitable neutralizing amines aremonoethanolamine, morpholine, dimethylamine, 3-methoxypropylamine,diethanolamine, diethylaminoethanol, dimethylpropanolamine,cyclohexylamine, 2-amino-2-methyl-1-propanol, triethanolamine,3-hydroxyquinuclidine, and 5-aminopentanol. Examples of the amine saltof high purity polymers are monoethanolamine salt of Polymer A,morpholine salt of Polymer A, and 3-methoxypropylamine salt of PolymerA. Neutralizing amines not only possess neutralizing ability, but alsohave metal-passivation effects.

Finally, if a polymer dispersant is acceptable based upon purity, cationconductivity, metal-oxide transport, and residence time, the selectedpolymer dispersant should be evaluated in a Constant Extension Rate Test(CERT). This test involves the measurement of the stress-corrosioncracking of a specimen comprised of Alloy 600, the principle tubingutilized within a steam generator of a nuclear power plant. The CERTtest requires Alloy 600 tubing having a gage length of 0.5 inch, a widthof 0.125 inches, and a wall thickness of approximately 0.045 inches.Test solutions were prepared in a stainless-steel feed tank, and thefeed tanks were purged of oxygen and filled with nitrogen prior to thepreparation of the test solution. A nitrogen-cover gas was maintained onthe test solution at all times, and the tests were performed on two testsolutions. The standard test solution #1 contained high-purity waterplus 100 parts per million 3-methoxypropylamine plus 10 parts permillion of N₂H₄ (hydrazine), and test solution #2 further included 312parts per million of the polymer dispersant, a concentrationapproximately 100 times greater than the recommended concentration to beused during reactor operations to demonstrate that metal degradationdoes not occur during normal operating conditions.

The tests were performed in a refreshed CERT autoclave with the testsolutions being prepared in stainless-steel tanks. The CERT tests wereperformed at a temperature of approximately 610° F. and at a pressure ofapproximately 1,900 psi, which is in excess of the saturation pressureat the test temperature. The test solutions were determined to have anion concentration of 25 parts per billion or less. The CERT testrequired a clean Alloy 600-test specimen to be placed in the rig, andthe autoclave sealed. Each solution separately was pumped through theautoclave at approximately 0.1 gallon per hour which flow rate providedan autoclave-residence time of two to four hours for each of the testsolutions. The autoclave was heated to approximately 610° F. during thetest, and the tube specimen was pulled at a constant cross-headdisplacement rate of approximately 5×10⁻⁷ inches per second, a strainrate of approximately 1×10⁻⁶. During each test the parameters, such asautoclave temperatures, autoclave pressure, specimen displacement,specimen load, and lab test time were recorded.

After the legs of the test specimen failed, the autoclave was cooled toroom temperature and the specimen removed. The failed specimens wereultrasonically cleaned and examined with a scanning-electron microscope.The fracture face of the legs were examined to determine the degree ofintergranular-stress-corrosion cracking which occurred during the test.Results of the stress-corrosion-cracking test indicated that the testsolutions did not visually appear to increase thestress-corrosion-cracking of Alloy 600, during a test time ofapproximately 150 hours per test. This test evaluation indicated thatthe tested polymer dispersant did not affect the failure rate of Alloy600 tubes.

In a typical 1100 megawatt nuclear steam plant, about 30,000 gallons perminute of feedwater is circulated through the steam generators, whichamounts to approximately 15,000,000 pounds of feedwater per hour throughthe generators. The secondary side of a nuclear steam generator isoperated in a range of about 500 to 1300 psi, with the preferred rangebeing between about 900 to 1300 psi. To maintain an effectiveconcentration of the polymer dispersant in the feedwater, approximately500 pounds of the concentrated polymer dispersant would be added to thefeedwater per month. This addition may be made either by injecting aslug amount of polymer dispersant rapidly into the feedwater or by theconstant addition to the feedwater through port 39, while maintaining aconcentration of the specified ions of less than 10 parts per billion,and preferably less than one part per billion ion concentration in theblowdown stream. The blowdown stream exits the secondary side 16 of thenuclear steam generator 14 through conduit 30 wherein the blowdownmaterial containing the removed and transported metal oxide is directedthrough a series of filter means 32, wherein the residual-polymerdispersant and complex metal-oxide/polymer dispersant from thedischarge-blowdown water is purified for recycling to the condenser 24.

In accordance with the present invention, the specialized filter meansmay include charcoal or activated-carbon filters, filter members havingpredetermined pore size and zeta potential, and demineralizationtechniques to remove residual polymer and complexed metal oxides forrecycling the blowdown water within the nuclear plant. The presentinvention further contemplates the removal of the residual-polymerdispersant and complexed metal-oxide/polymer dispersant from theblowdown waste utilizing the method of flocculation and coagulation andreverse osmosis for either recycling or ultimate discharge to areceiving stream 38. These methods of filtration and purificationrespectively remove the residual-polymer dispersant and complexedmetal-oxides/polymer dispersant from the discharge-blowdown water forrecycling through the condenser to the feedwater conduit.

The novel method of preventing the formation of sludge, corrosion, ormetal-oxide deposits within the secondary side of nuclear steamgenerators during the continued operation of the generator utilizes theinjection of the high-purity polymer dispersant and/or sludgeconditioners into the feedwater. The polymer dispersant possesses achemical purity of less than 10 parts per billion of ions selected froma group comprising sodium, potassium, chloride, sulfate, phosphate,magnesium, calcium, and silicate as measured in the blowdown stream. Thechemical purity of the feedwater and polymer dispersant and the cationconductivity may be determined through sampling ports 40 and 19′,respectively. Variations of the novel method further includes the stepof discharging the blowdown water from the secondary side of the nuclearsteam generator and then filtering and removing the residual-polymerdispersant and complexed metal oxide from the blowdown stream forrecycling as feedwater entering the secondary side of the nuclear steamgenerator. The above-identified process may include also the utilizationof specialized filter means having predetermined pore size and zetapotential and filter purification means such as charcoal, activatedcarbon, flocculation, coagulation, reverse osmosis, and ultrafiltrationto remove the polymer dispersant and complex metal oxide prior toultimate discharge to a receiving stream.

While several embodiments of the invention have been described in thepresent specification, it is clearly understood that the embodiments aresusceptible to numerous changes apparent to one skilled in the art, and,therefore, we do not wish to be limited to the details shown ordescribed but intend to show all changes and modifications which comewithin the scope and parameters of the appended claims.

We claim:
 1. A high-purity polymer dispersant and sludge conditioner foraddition to the feedwater entering the secondary side of a nuclear steamgenerator during the continuing operation of the generator forminimizing the accumulation of metal-oxide deposits within the secondaryside of the nuclear steam generator, wherein said high-purity polymerdispersant and sludge conditioner is selected from a group consisting ofacrylic acid polymer, methacrylic acid polymer, acrylate polymer,methacrylate polymer, copolymers, acrylate/acrylamide copolymer,acrylate/methacrylate copolymer, and mixtures thereof and wherein saidhigh-purity polymer dispersant and sludge conditioner has a contributionof ions of about 10 parts per billion or less each of sodium, potassium,calcium, magnesium, chloride, sulfate, silicate, and phosphate.
 2. Thepolymer dispersant and sludge conditioner in accordance with claim 1,wherein said contribution of each ion to said blowdown is about one partper billion or less.
 3. The polymer dispersant and sludge conditioner inaccordance with claim 1, wherein said polymer dispersant and sludgeconditioner possesses a metal oxide to polymer ratio of about 1 to 1,000parts polymer to treat one part metal oxide.
 4. The polymer dispersantand sludge conditioner in accordance with claim 1, wherein the preferredrange of the metal oxide to polymer ratio is about 1 to 25 parts polymerto treat one part metal oxide.
 5. The polymer dispersant and sludgeconditioner in accordance with claim 1, wherein said group furtherincludes sulfur-containing and phosphorus-containing functional groupsand mixtures thereof.
 6. The polymer dispersant and sludge conditionerin accordance with claim 5, wherein said sulfur-containing functionalgroup is selected from a group consisting of sulfonated styrenepolymers, copolymers, terpolymers, and mixtures thereof.
 7. The polymerdispersant and sludge conditioner in accordance with claim 1, whereinsaid polymer dispersant and sludge conditioner has a weight-averagemolecular weight of about 1,000,000 or less.
 8. The polymer dispersantand sludge conditioner in accordance with claim 1, wherein said polymerdispersant and sludge conditioner has a weight-average molecular weightof between about 70,000 to 150,000.
 9. The polymer dispersant and sludgeconditioner in accordance with claim 1, wherein said high-purity polymerdispersant and sludge conditioner is substantially free of inorganicsolids.
 10. The polymer dispersant and sludge conditioner according toclaim 1, wherein the initiator and chain terminator of the polymerprovides a polymer which is substantially free of inorganic solids, saidinitiator being selected from a group consisting of benzoyl peroxide,acetyl peroxide, succinic acid peroxide, lauroyl peroxide, decanoylperoxide, hydrogen peroxide, 2,2′ azobis (2-methylpropanenitrile), 2,2′azobis (2-methylbutanenitrile), t-butyl peroctoate, t-butyl peroxyisobutgrate, t-butyl peroxyprivalate, and 4,4′-azobis (4-cyonovalericacid), and mixtures thereof.
 11. The polymer dispersant and sludgeconditioner in accordance with claim 1, wherein the polymer isneutralized with an amine.
 12. The polymer dispersant in accordance withclaim 11, wherein said amine is selected from a group consisting ofmonoethanolamine, morpholine, diethylaminoethanol, dimethylamine,diethanolamine, 3-methoxypropylamine, dimethylpropanolamine,cyclohexylamine, 2-amino-2-methyl-1-propanol, triethanolamine,quinuclidine, 5-aminopentanol, and mixtures thereof.
 13. A high-puritypolymer dispersant and sludge conditioner for addition to the feedwaterentering the secondary side of a nuclear steam generator during thecontinuing operation of the generator for removal of existingmetal-oxide deposits from the secondary side of the nuclear steamgenerator, wherein said high-purity polymer dispersant and sludgeconditioner is selected from a group consisting of acrylic acid polymer,methacrylic acid polymer, acrylate polymer, methacrylate polymer,copolymers, acrylate/acrylamide copolymer, acrylate/methacrylatecopolymer, and mixtures thereof and wherein said high-purity polymerdispersant and sludge conditioner has a contribution of each ion ofabout 10 parts per billion or less of sodium, potassium, calcium,magnesium chloride, sulfate, silicate, and phosphate.
 14. The polymerdispersant and sludge conditioner in accordance with claim 13, whereinsaid contribution of each ion to said blowdown is about one part perbillion or less.
 15. The polymer dispersant and sludge conditioner inaccordance with claim 13, wherein said polymer dispersant and sludgeconditioner possesses a metal oxide to polymer ratio of about 1 to 1,000parts polymer to remove one part metal oxide from the secondary side ofthe nuclear steam generator.
 16. The polymer dispersant and sludgeconditioner in accordance with claim 13, wherein the preferred range ofthe metal oxide to polymer ratio is about 1 to 25 parts polymer toremove one part metal oxide.
 17. The polymer dispersant and sludgeconditioner in accordance with claim 13, wherein said polymer dispersantand sludge conditioner has a weight-average molecular weight of about1,000,000 or less.
 18. The polymer dispersant and sludge conditioner inaccordance with claim 13, wherein said polymer dispersant and sludgeconditioner has a weight-average molecular weight of between about70,000 to 150,000.
 19. The polymer dispersant and sludge conditioner inaccordance with claim 13, wherein said high-purity polymer dispersantand sludge conditioner is substantially free of inorganic solids. 20.The polymer dispersant and sludge conditioner according to claim 13,wherein the initiator and chain terminator of the polymer provides apolymer which is substantially free of inorganic solids, said initiatorbeing selected from a group consisting of benzoyl peroxide, acetylperoxide, succinic acid peroxide, lauroyl peroxide, decanoyl peroxide,hydrogen peroxide, 2,2′ azobis (2-methylpropanenitrile), 2,2′ azobis(2-methylbutanenitrile), t-butyl peroctoate, t-butyl peroxyiso butgrate,t-butyl peroxyprivalate, and 4,4′-azobis (4-cyonovaleric acid), andmixtures thereof.
 21. The polymer dispersant and sludge conditioner inaccordance with claim 13, wherein the polymer is neutralized with anamine.
 22. The polymer dispersant and sludge conditioner in accordancewith claim 21, wherein said amine is selected from a group consisting ofmonoethanolamine, morpholine, diethylaminoethanol, dimethylamine,diethanolamine, 3-methoxypropylamine, dimethylpropanolamine,cyclohexylamine, 2-amino-2-methyl-1-propanol, triethanolamine,quinuclidine, 5-aminopentanol, and mixtures thereof.